Hydraulically-operated spudding mechanism for cable-tool drills



1958 T. N. HUDSON ET AL 2,865,603

HYDRAULICALLY-OPERATED SPUDDING MECHANISM FOR CABLE-TOOL DRILLS FiledFeb. 8, 1954 L 36(Smumc: VALVE) 27 (R5515 A c5 JAB'IB K5 START VALVE)IIIIIIII/I/A LILJS Tom N- Huvsou,

HERBERT w-Thomsukq ALBERT c. HAl-acH,

INVENTORS.

9 w M 14 71 W HYDRAULICALLY-OHERATED SPUDDING MECHANISM FOR iIABLE-TOQLDRILLS Tom N. Hudson, Milwaukee, and Herbert W. Thornburg and Albert C.Haiscn, South Milwaukee, Wis, assignor to Bucyrns-Erie Company, outhMilwaukee, Wis, a corporation of Delaware, and Tom N. Hudson, Milwaukee,Wis.

Application February 8, 1954, Serial No. 403,693

Claims. cr. 255-40 This invention relates to new and usefulhydraulicallyoperated spudding mechanism for cable-tool drills, andconstitutes an improvement over the drill shown, described, and claimedin the copending application of one of the three joint inventors of thepresent invention, said copending application being Serial No. 251,499,now Patent No. 2,749,090, filed October 16, 1951, by Tom N. Hudson, forCable-Tool Drill, to which copending application reference may be madefor anything not fully described and shown herein.

Spudder-type cable-tool drills, per se, are well known in the art. I

In such drills, a rope passes from a winch-drum on the main frame,thence over or under one or more sheaves, one of which is usually at theupper end of a mast, and from this latter sheave vertically downwardinto the hole which is being drilled in the ground. At the lower end ofthis rope is a string of drilling tools, terminating in a percussionbit. One of the sheaves, over or under which the rope passes, isreciprocable by appropriate associated means, whereby the bit is rapidlyalternately raised and then dropped, to drill the hole, which operationis known in the trade as spudding.

It is the principal object of the present invention to devise anautomatically self-synchronizing hydraulicallyoperated cable-tool drillwith superior operating characteristics.

More particularly the present invention is directed to: providingimproved automatic reversing means for the spudding mechanism, such thatreversal will take place very quickly shortly near the end of the downstroke of the bit, and yet will take place gradually near the end of theup-stroke of the bit.

Still more particularly the present invention is directed to:eliminating all manual control valves from the main circuit; setting upa pilot circuit wholly independent of the main circuit; controlling thepump-to-cylinder circuit by opening and closing a by-pass therefrom,leaving the pump-to-cylinder circuit itself always open; preventing thespudding-sheave from overrunning the spudding-cable,

- and vice versa; and a safety device to reduce the main circuitpressure to substantially zero upon shutting off or failure of pilotpressure.

The present invention consists in the noval parts and in the combinationand arrangement thereof, which are defined in the appended claims, andof which one embodiment is exemplified in the accompanying drawing,which is hereinafter particularly described and explained.

Throughout the description, the same reference number is applied to thesame member or to similar members.

The single figure shows the hydraulic circuits and associated mechanismof the present invention, largely conventionalized. Other conventionalparts of the drill mechanism are not shown, being well known in the art.

From a winch-drum 11 on the main frame (not shown), a cable 12 extendsupwardly and over a spudding-sheave 13, journaled in a sheave-block 14,which is slidably mounted at the top of a mast (not shown) in any con-Patented Dec. 23, 1958 venient manner for limited sliding up and down.Thence the cable extends downwardly to support and reciprocate adrill-bit 15, shown in Well-hole 16, which it is digging.

At the foot of the mast (not shown), supported by the main frame (notshown), there is a hydraulic cylinderpiston assembly 17, of which thepiston-rod 18 extends up the mast to support and reciprocatesheave-block 14.

Tank 19 is a tank for hydraulic fluid, which supplies, and serves as asump for, the hydraulic fluid which circulates in the main circuit andthe pilot circuit of the present invention.

There will now be described the main hydraulic fluid system.

Main pump 21 is connected on its intake side to the fluid in tank 19 bypipe 20; and on its output side, through pipe 22 and a part of areversing-valve 23 (hereafter referred to, as the spudding-valve) andpipe 24, to cylinder-piston assembly 17. The control of fluid-flowthrough the just-described circuit from pump 21 to cylinder 17 iseffected not by closing and opening this circuit, but rather by closingand opening a by-pass to sump 19 through valve 23 (as will be describedhereinafter).

25 is the pilot-pressure-closed spring-opened plunger of spudding-valve23. Normally open, it permits the passage of fluid from pipe 22 throughopening 26 to resistancevalve 27, and thence through return-pipe 28,back to tank 19. Thus it will be seen that valve 23 takes the place of aconventional reversing-valve, at a gain in simplicity of piping. Eithertype of valve could be pilot-pressure shifted in both directions, butthis would not only complicate the piping, but also would eliminate thefollowing safety feature. In event of shut-oft or break-down ofpilot-pressure, spudding-valve 2.3 is opened by its spring,

and the bit will come to rest at the bottom of the stroke. Whereas,without this feature, the bit might come to rest at the top of thestroke; and then upon the resulting stalling of the engine, or theshutting oif of the engine, the bit would drop uncontrolled.

Either type of valve could be pilot-pressure shifted in eitherdirection; but to retain the safety feature, either type of valve wouldhave to be shiftable into its bit raising position by pilot-pressure,and into its bit-lowering position by some means not involvingpilot-pressure, such as main-pressure or a spring, the latter beingpreferable.

Valves 23 and 27 are shown built integral as a single unit. But this ismerely for structural convenience; they -could just as well be builtseparately, and connected by aprpe.

29 is the pilot-pressure-closed main-pressure-opened plunger ofresistance-valve 27. When pilot-fluid is no longer supplied to thisvalve, and spudding-valve 23 is open, seepage of pilot-fluid aroundplunger 29 and/or through bleeder 55 will reduce to substantially zerothe resistance to the by-passing of fluid from pump 21, through pipe 22,valve 23, opening 26, valve 27, and pipe 28, back to tank 19; also toexhausting cylinder 17 through valve 23, etc.

But when spudding-valve 23 is open, and resistancevalve 27 is under theinfluence of pilot-pressure, plunger 29 of the latter sets up apredetermined back-pressure to this by-passing. The object of thisback-pressure is to prevent free fall of sheave 13 during lowering, andthus prevent this sheave from overrunning cable 12. In this connection,resistance-valve 27 can be adjustably regulated by relief-valve 46, in amanner hereinafter described.

Resistance-valve 27 .also cooperates with choke-valve 41, in a mannerhereinafter described.

Resistance-valve 27 a.so supplies the following safety feature. in theevent the bit is prevented from descending in the down stroke by someexternal cause (such as sticking in the hole), the back pressure in themain circuit sheave; accordingly, were itnot for 12 would overrun sheave13 at the top of the stroke.

.pressure when the machine is not spudding. Secondly,

'pilot-pressure-closing establishes a substantially constant resistanceto main-fluid flow, regardless of the volume of fluid passing-throughthe resistance-valve.

3%? is merely a vent-pipe for the upper part -17.

There will now be described the pilot fluid system.

For convenience in studying the figure, the pilot pipes are shownsmaller than the main pipes.

31 is the pilot-pump. It is connectedon its intake side to the fluid intank 19 by pipe 32, and on its output side to start-stop valve 33 bypipe 34. Pipe 35 is the returnpipe from start-stop valve 33 to'tank 19.i

36 is a valve. preferably of a particular typeknown as a sequence-valve(see later herein), connect-ed to valve 33 by pipe 37.

Valve 33 can be any convenient kind of valve, such that when set tostop, it connects pipe 34 to pipe 35; and when set to start, it connectspipe 3 to pipe 37.

38 is a reversing-valve (hereinafter referred to, as the pilot-valve),of any convenient type, connected to sequence-valve 36 by pipe 39. Frompilot-valve 33, pipe cylinder at) extends to spring-setpressure-released choke-valve 41,

from which valve pipe 42 extends to the operating end of plunger 25 ofspudding-valve 23. For pipe 43, see later herein.

, The operation of choke-valve 41 is as follows. When fluid is flowingtherethrough from pipe 49 to pipe 42, the pressure of this fluid on theplunger of this valve will overcome the pressure of the spring to openthe valve wide, away from the screw. But when fluid is flowing in theopposite direction, the spring will close the valve (not completely, butrather merely until it contacts the screw) to a narrow bleeder-oriflce,the

size of which is determined by the setting of the screw.

The function of choke-valve 41 is to permit free flow ofpilot fluid tospudding-valve 23, to actuate plunger 25 toclose spudding-valve 23, whenrotary member fit) of pilot-valve 38 is in its full-line position; butto bleed back 'fluid through an adjustable orifice from spudding-valve23, when rotary member 5% is in its dotted-line position, so as toprevent too rapid opening of spudding-valve 23- near the top of thepiston stroke. The relatively gradual opening of spudding-valve 23,gradually decreases the pressure in the bottom of cylinder 17, untilthis pressure is reduced to the pressure-level established byresistancevalve 27, whereupon the resistance-valve takes over. Thiscontrolled opening of the spudding-valve also controls the surgeof fluidthrough opening 36 which might ding-valve 23 opens when sheave 13 andbit 15 are moving upward, the bit at twice the velocity of thechoke-valve 4-1, cable Thus resistance-valve 27 and choke-valve 41perform similar functions: the former, preventing sheave 13 fromvoverrunning cable 12 during lowering; the two together,

preventing cable 12 from overrunning sheave 13 at the top of the stroke.The need for both expedients is due to the travel-ratio of tools andsheave. This requires that, in

' order to keep cable and sheave in phase, the gravitational pull on thesheave and associated parts must be opposed (so as to reduce theneteffect to one-half or less) during otherwise unbalance the predeterminedsetting of resisti ance-valve 27. In the spudding cycle of this drill,spud- I 4 both lowering and near the end of raising. This isaccomplished during lowering by braking the escape of fluid from thecylinder, and at the top of the stroke by reducing the admission offluid to the cylinder gradually instead of abruptly.

Pilot-valve 38 is also connected to tank 19 by pipe 43. The fourth portof pilot-valve 38 is plugged, but would be connected by a pipe to theleft-hand end of plunger of spudding-valve 23, if that valve were of asort operated in both directions by pilot-pressure.

Pipe dd extends from sequence-valve to the operating end of plunger 29of resistance-valve 27. From pipe 44 pipe 45 extends to adjustablerelief-valve 46 (which valve serves to regulate resistance-valve 2.7, aswill be hereinafter explained), whence pipe 47 connects to tank 1*? inany convenient manner, as via pipe 43.

Pipe 33 is merely a drain-pipe for valve 36. Passage 4% insequence-valve 36 is to operate-the plunger in this valve whenever pipe39 is blocked by valv'e38, or otherwise as hereinafter mentioned. Itshould be noted that pipe 39 is always open to pipe 37, and hence thecircuit of these two pipes goes through sequence-valve 36 merely forconvenience; it could just as well lay-pass valve 36. The sequence-valveas above described is considered preferable at this place to aconventional adjustable reliefvalve, due to the fact that what is neededat this pointis a relief-valve whose opening is'ccntrolle d by thepressure merely in pipe 37, and is not influenced by the back-pressurein pipe 44.

Also piped lcould extend from the plugged port (no longer plugged) ofspudding-valve 38, instead of from sequence-valve 36; in which event thelatter would instead discharge into some pipe leading to tank 19.

Reverting now topilot-valvefifi, it will be seen that this valveincludes a rotary member 50 which savings back and forth through about45 degrees, under the influence of trip-dog 51. The two extremepositions of rotary member Sil are shown; one position full, the otherposition dotted. The fact that trip-dog 51 controls rotary member 56 isindicated by the dot-dash line which connectsthcir respective centers onthe drawing.

Trip-fingers 52 (black) and '53 (white) are adjustably secured to-rod54, which reciprocates with piston-rod 18. Black trip-flnger 52 is inthe same plane as the black prong of trip-dog 51. White trip-finger 53is in the-same plane as the white prongof the trip-dog; but thesetwoplanes are different. As. shown in the figure, pistom'rod 18 has justcompleted its descent, and black trip-finger 52 has recently engagedtheblack prong of trip-dogfi l, and thereby has just completed trippingtrip-dog'il. into its shown position, thus shifting rotary member 51) ofpilot-valve 38 into itsshown full-line position.

The pressures of certain of the valves is important, as will now beexplained.

The pilot-fluid pressure acting on plunger 25 of spudding-valve23 mustbe of such magnitude as to overcome the force of the plunger-spring, andthe inertia of the plunger to shift the plunger quickly to its closedposition. This pressure is regulated by the'adjustment ofsequencevalve36. When the pressure in pipes-37 and 35 exceeds the pressure-settingIof sequence-valve 36, eitherv when plunger 25 has been shifted to itsclosed position or when pipe 39 is blocked by pilot-valve 33,sequence-valve 36 beyond .this'point to retard the fall of the bit tosatisfy 57, certain operating conditions, as is well understood in theart.

The operation of the drill shown and described herein should be readilyevident from the figure'an'd the foregoing description, but neverthelesswill now be outlined.

Assume everything tobe in the positions shown in the figure.

Both pumps are started.

Pilot fluid circulates unrestricted through pipe 32, pump 31, pipe 34,start-stop valve 33, and pipe 35, back to tank 1?.

Main fluid circulates unrestricted through pipe 20, pump 23, pipe 22,spudding-valve 23, opening 26, resistance-valve 2'7 (which offerssubstantially no resistance, as there is no pilot-pressure behind itsplunger 29), and pipe 28, back to tank 19.

Thus the machine is idling.

Start-stop valve is now thrown to start position, thus shuntingpilot-fluid through pipe 37, sequence-valve 36, pipe 3%, pilot-valve 38,pipe 40, choke-valve 41 (which never opposes flow in this direction),and pipe 42, to spudding-valve 23, the plunger 25 of which it shiftsabruptly to the left, thus closing this valve. Main fluid, prevented bythe closing of the spudding-valve from free return to the tank, proceedsthrough pipe 24 into cylinder 17 thus raising the piston, and hencesheave 13, and bit 15.

Having performed the closing of spudding-valve 23, the pilot fluid hasno-where to go, except through passage 2-9 to shift the plunger ofsequence-valve 36 to the left, which it does, thereby permitting itselfto'escape through pipe 44, then first closing valve 27 (the position ofwhich, at this-stage of the cycle, is immaterial), and thereafterescaping through pipe 45, relief-valve 46, pipe 47, and pipe 43, back totank 19.

Shortly before piston-rod 18 reaches the top of its more, whitetrip-finger 53 engages the white prong of trip-dog $1, rotating thisdog, and hence member 50 of pilot-valve 38, approximately 45 degreesclockwise into the position shown dotted, thus connecting pipes 48 and43 through this valve. Pilot pressure from pump 31 still remainsblocked, but now by pilot-valve 38.

There being now no longer any pilot-pressure against the right-hand endof plunger 25 of spudding-valve 23, the spring forces this plunger tothe right (but slowly, due to the back-pressure in pipe 42, set up byflow resistance in choke-valve 41). The pilot-fluid'displaced by thisshift of the plunger, backs up in pipe 42, and after oozing throughchoke-valve 41, passes, by way of pipe 40, pilot valve 38, and pipe 3-3,to tank 19.

The opening of spudding-valve23 permits main-pressure from pump 21 tocirculate back to tank 19, as it did when the machine was idling, butnow not freely, for pilot-pressure in pipe holds plunger 29 ofresistancevalve 27 partly closed.

The weight of the bit 15, and of the sheave l3 and associated parts,forces down the piston, and thus forces fluid in gradually increasingvolume, out of cylinder 17,

into pipe 24, and into spudding-valve 23, where this fluid reboundsfr'omthe bottom of the hole; whereas the rejoins the main pump fluid on itsway back totank 19,

through spudding-valve 23, resistance-valve 27, etc.

Shortly before piston-rod 13 reaches the bottom of its stroke, blacktrip-finger 52 engages the back prong of trip-dog 51, rotating this dog,and hence member of pilot-valve 38, approximately 45 degreescounterclockwise back into its initial position (shown in full lines),thus again connecting pipes 39 and 4% through this valve.

Pilot-pressure, through pipe 49, choke-valve 41 (which does not opposeflow in this direction), and pipe 42, to spudding-valve 23, shifts theplunger 25 abruptly to the left.

This is where we came in.

The above-described cycle is repeated again and again, until stop-startvalve is manually closed.

It should be noted that the reversal at the bottom of the stroke isalways quick, thus not retarding the working fall of the bit, andassuring a sharp pick-up of the bit as it v versal at the top of thestroke is slow enough to prevent the rising "cable from overrunning thesheave; and that the down-travel of the piston accelerates slowly enoughto prevent falling sheave from overrunning the cable.

It should be noted also that a single-acting cylinderpiston is employed,reciprocation being accomplished by opposing the weight of the tools,cable, piston, piston rod, sheave-block, sheave, etc., by automaticallyalternatingtwo alternative hydraulic pressures in the cylinder;hydraulic pressure overbalancing weight during raising, and weightoverbalancing hydraulic pressure during lowering.

The system of the present invention is automaticallyself-synchro-nizingzi. e., it eliminates the need (which exists inconventional drills of the prior art) of requiring the operator tocarefully'control the spudding speed, so as to adapt it to changingconditions in the hole, such (for example) as the extent of bottoming ofthe bit.

In the claims, except and unless where specifically stated tothecontrary, the mention of a single element performing severalfunctions shall be interpreted as reading on several such elements, andthe mention of several similar elements performing functions capable ofbeing performed by a single such element shall be interpreted as readingon a single such element.

Elements shown and described as being built separate or integral, can bebuiltintegral or separate, except and unless where specifically statedto the contrary.

Although herein the main system and the pilot system are shown anddescribed as independent systems, each with its 'ownpressure-source (i.e., pump), this independence is not to be read into any claim which doesnot so specify. And even where so specified, this does not exclude thepossibility of a common sump and common return conduits thereto.

In the claims the word fluid" is to be understood to include pneumaticfluid as well as hydraulic fluid. In the case of pneumatic fluid the-sump could of course be the atmosphere.

One embodiment of the invention having now been described, it is to beunderstood that the invention is not to be considered limited to thespecific form or arrangement of parts herein shown and described. Morespecifically, whenever in the specification some improved substitute fora conventional element is shown and described, a limitation to suchimproved substitute is not to be read into any claim which does not sospecify.

What isclaimed is:

1. In an automatically. self-synchronizing spudding mechanism forcable-tool drills, the combination of:

cable-engaging means to impart vertical reciprocating motion to apercussion-drill bit suspended by a cable; a fluid-pressure-actuatedsingle-acting cylinder-piston assembly, acting in opposition to gravity,to reciprocate the cable-engaging means; source means for creating fluidpressure; a sump; a main-fluid system, comprising a first main passageextending from the source means to the cylinder-piston assembly, and asecond main passage extending from the first main passage to the sump; aspudding-valve, interposed between the first and second main passages,for alternatively closing and opening the second Y main passage withrespect to the first main passage, and

'thereby'respectively causing main fluid to flow alternatively from (1)the source means to the cylinder-piston assembly through the first mainpassage to actuate the cylinder-piston assembly to raise the bit and (2)from .the cylinder-piston assembly and the source means through thesecond main passage to the sump to permit gravity to lower the bit;automatic control means for alternatively setting the spudding valve inwear the other of its two alternative positions, responsive to theposition and motion of the cable-engaging means, the

first-mentioned setting being effected when the cable-:

engaging means reaches a predetermined bit-lowering position, and thesecond-mentioned setting being elfectcd when .the cable-engaging meansreachesa predetermined bit-raising position; said automatic controlmeans including: a pilot valve, a first pilot passage leading from thesource means to the pilot valve, a second pilot passage leading from thepilot valve to the spudding valve to introduce fluid to said spuddingvalve to actuate the same, a third pilot passage leading from the pilotvalve to the sump, said pilot valve being shiftable to two alternativesettings to alternatively direct to the spudding-valve through thesecond pilot passage pilot fluid derived from thesource means throughthe first pilot passage, or direct to the sump through the third pilotpassage pilot fluid exhausted from the spudding-valve through the secondpilot passage, said pilot valve blocking in its last-mentionedalternative setting flow of pilot fluid in the first pilot passage andthereby causing therein an increase in pilot fluid pressure, and meansresponsive to the movement of the cables-.ngaging means to shift thepilot valve; a resistance valve interposed in the main exhaust passagefrom the cylinder-piston assembly that includes the second main passage,said resistance valve having a restricted passage to resist when partlyclosed-the exhaust flow of fluid through said main exhaust passage: andbeing shiftable to open responsive to exhaust pressure in said mainexhaust passage; a fourth pilot passage, leading from the first pilotpassage to the resistance valve, to introduce fluid to said resistancevalve to actuate the same to close; a bypass leading from the fourthpilot passage toward the sump; a relief valve interposed in the bypassand actuable by fluid pressure in the fourth pilot passage to admitfluid therefrom into the bypass and thereby maintain pressure on theresistance valve to actuate the same to close in opposition to theexhaust flow and thereby maintain a predetermined exhaust'pressure inthe main exhaust passage; and valve means interposed in the fourth pilotpassage for admitting fluid through the fourth pilot passage to theresistance valve whenever the pilot valve is set to block the fluid flowin the first pilot passage and thereby cause an increase in fluidpressure in said passage and in the fourth pilot passage to therebymaintain a retarding fluid pressure on the resistance valve when thecable-engaging means reaches its said predetermined bit-raisingposition.

2. A spudding mechanism according to claim 1, still furthercharacterized by the fact that the valve means for admitting fluidthrough the fourth pilot passage comprises: a sequence valve in saidpassage, said sequencevalveheing actuable by pressure in the first pilotpassage ,to admit pilot-fluid from the first pilot passage throughsaidfsequence valve into the fourth pilot passage.

, 3. A spudding mechanism according to claim 2, further characterized bythe fact that the sequence-valve includes means biasing thesequence-valve in opposition to the pressure fluid in the first pilotpassage for causing the seguence-valve to open responsive to the degreeof pressure in the first pilot passage independent of the degree ofpressure in the fourth pilot passage.

4. A spudding mechanism according to claim 1, further characterized byhaving a choke-valve interposed-in the return passage whichcomprises thesecond pilot passage, the pilot. control means, and the third pilotpassage, saidchoke-valve being adapted to retard the opening of thespudding-valve when the pilot-valve is set topermit the return flow offluid from the second pilot passage to the third pilot passage, andthereby prevent unbalancing of the resistance-valve by a surge ofexhaust fluid through the second main passage.

5 .1111 an automatically self-synchronizing spudding mechanism forcable-tool drills, the combination of: cable-engaging means to impartvertical reciprocating motion to a percussion-drill bit, suspended by acable; a fluid-pressure-actuated single-acting cylinder-piston assemblyto reciprocate the cable-engaging means; fluid pressure source means; asump; a main fluid passage from the source means to the cylinder-pistonassembly, and a second main fluid passage, from the first main fluidpassage to the'sump; a spudding valve, interposed between the first andsecond main fluid passages, for alteruatively closing and opening thesecond main fluid passage; automatic control means including a shiftablefluidpressure pilot-control means for alternatively setting the spuddingvalve in one or the other of its two alternative positions, responsiveto the position and motion of the cable-engaging means, thefirst-mentioned setting being effected when the cable-engaging meansreaches a predetermined bit-lowering position, and the second-mentionedsetting being effected when the cable-engaging means reaches apredetermined bit-raising position, and means responsive to the movementof the cable-engaging means to shift the pilot control means the passageof pressure fluid through said pilot control means being blocked whenthe cable-engaging means is in its said predetermined bit-raisingposition; resistance-valve means interposed in the second main fluidpassage and having a restricted passage for resisting in varying degreeswhen partly closed the exhaust flow of fluid therethrough and beingshiftable to open responsive to exhaust pressure in said second mainfluid passage; a pilot passage connecting said resistance valve to thepilot-control means for introducing fluid to said resistance valve toactuate the same to close; .a bypass leading from the pilot passagetoward the sump; a relief valve interposed in the bypass and actuable byfluid pressure in the pilot passage to admit fluid therefrom into thebypass and thereby maintain pressure on the resistance valve to actuatethe same to close in opposition to the exhaust flow and thereby maintaina predetermined exhaust pressure in the second main fluid passage; andvalve means, interposed in said pilot passage for admitting fluidtherethrough to the resistance-valve whenever the means responsive tothe movement of the cable-engaging means shifts the pilot control meansto block the passage of fluid therethrough when the cable-engagingmeansreaches its said predetermined bit-raising position.

References Cited in the file or" this patent UNITED STATES PATENTS801,528 Klay Oct. 10, 1905 1,273,618 Julien et al July 23, 19182,026,853 Smith Jan. 7, 1936 2,073,809 Salentine Mar. 16, 1937 2,220,271Peyton et al Nov. 5, 1940 2,282,977 Mast May 12, 1942 2,572,748 Noll eta1 Oct. 23, 1951 2,749,090 Hudson June 5, 1956

